The Motion Pictures Experts Group-2 (MPEG-2) standard is used to supply a stream of digital data to digital receivers such as set-top boxes (STB) and digital television (DTV). The digital data takes two forms. One form of the digital data stream is called a transport stream (TS) and is intended to carry multiple programs. The other form of the digital data stream is called a program stream (PS) and is intended to carry one program. The MPEG-2 standard also allows conditional access (CA) of the program content by providing mechanisms to support the use of proprietary encryption and access functions. These mechanisms are defined only for transport streams.
Digital receiver units receive MPEG-2 transport streams and allow selection and play of programs. Digital receiver units may also receive program streams (PS) from storage devices. MPEG-2 program streams contain one program. Receiver units equipped with storage subsystems further allow recording of programs for playback at a later time.
For programs delivered as a transport stream, MPEG-2 fully specifies the encrypted data structure to allow a service provider to enforce conditional access on any program in the stream. Unfortunately, MPEG-2 does not fully specify the encrypted data structure for a program stream. Rather, it is left to the storage subsystem of the receiver to provide conditional access control. Consequently, receiver manufacturers are presented with the problem of efficiently implementing features such as selective single program recording with conditional access control on the recorded program.
Currently, three approaches to the problem of selective recording of programs while preserving conditional access exist. The first approach is to store the entire MPEG-2 transport stream. However, the first approach requires large amounts of storage, especially for services that supply large numbers of programs in a single transport stream.
The second approach is to decrypt the program of interest and then store the decrypted program in a receiver manufacturer proprietary format. However, the second approach takes the control away from the service provider and may not supply a sufficiently robust encryption.
The third approach is to decrypt the program of interest and store the program in the “clear,” that is, in an unencrypted format. However, the third approach may not be acceptable to the service provider or the owner of the copyright of the program being thus recorded.